1. Field of the Invention
The present invention relates generally to a reception apparatus and method in a mobile communication system. In particular, the present invention relates to a reception apparatus and method of a mobile station in a Software Defined Radio (SDR) mobile communication system.
2. Description of the Related Art
A mobile communication system that began with an analog system in the 1980s has evolved into a digital system such as Code Division Multiple Access (CDMA) and, in the 1990s, the Global System for Mobile communication (GSM), which is a 2nd generation mobile communication system evolved as the manufacturing cost of digital circuits decreased and users required higher call quality. As digital mobile phones are characterized by low-priced terminals, high quality-of-service (QoS), low call charges, and fundamental data communications, the number of mobile communication subscribers has been rapidly increasing in recent years.
FIG. 1 is a block diagram illustrating a structure of a reception apparatus for a mobile station in a general mobile communication system. The reception apparatus of a mobile station is comprised of a radio frequency (RF) processor 20 for converting an RF signal received via an antenna 10 into a digital signal, and a modem 100 realized with hardware, for demodulating the digital signal. The modem 100 is realized with Application Specific Integrated Circuits (ASICs) because it can process complicated calculations in real time in order to accurately receive a reception signal at a time desired by a base station.
A signal passed through an RF subsystem 21 is input to an analog-to-digital (A/D) converter 22, and the A/D converter 22 outputs digital quadrature (I,Q) data. The output data of the A/D converter 22 is sampled by a chip×8 clock, and despread with a corresponding Pseudo-random Noise (PN) code by a despreader 112. The output signal of the despreader 112 is input to a channel measurer 115 and a dechannelizer 113. The channel measurer 115 generates I and Q signals for channel compensation by accumulating input signals for an accumulation period determined according to a characteristic of a filter, and the dechannelizer 113 Walsh-decovers an input signal by multiplying the input signal by a corresponding Walsh code. The I and Q output signals of the dechannelizer 113 and the channel measurer 115 are subject to channel compensation in a demodulator 114 through a complex multiplication. The demodulated signal output from the demodulator 114 is subjected to symbol combining in a combiner 120, and then descrambled by a scrambling code generated by a long code generator 140. A forward link power controller (FLPC) 130 generates a forward link power control signal. A reference time generator (RTG) 150 has the function of generating a reference time of the mobile station, and generates an 80-ms boundary, a 1.25-ms signal, and a 20-ms signal.
Such a mobile station for mobile communication should necessarily satisfy the light, low-power, low-price requirements, and in the near future, it should also satisfy a fast time-to-market requirement, which is a first requirement. Although this requirement should be satisfied even in designing a conventional terminal, it is now at issue because changes in the market occur faster than ever before. A second requirement is a flexibility requirement. In order to adapt to various standards currently in use or in development, the structure of the mobile station should have high flexibility. This is related to the first requirement, because a developed terminal, if it has flexibility, can simply identify a new standard. Such requirements are necessary for seamless roaming between standards and regions.
However, a 2nd generation mobile phone cannot receive a global roaming service because respective regions use different standards. The recent global mobile communication environment is formed by 2nd generation digital systems in various modes, such as GSM in Europe, Digital-Advanced Mobile Phone System (D-AMPS) in North America, Personal Digital Cellular (PDC) and Personal Handyphone System (PHS) in Japan, and IS-95 CDMA in South Korea. Also, a 3rd generation broadband International Mobile Telecommunication-2000 (IMT-2000) standard that continued to evolve with a unified standard aiming at the global roaming service has been divided into 3rd Generation Partnership Project 2 (3GPP2) cdma2000 in North America and 3rd Generation Partnership Project (3GPP) Wideband CDMA (W-CDMA) in Europe and Japan, and the different standards are expected to be regionally commercialized, or are being commercialized presently. Because the regional 2nd generation and 3rd generation mobile communication standards require independent transmission/reception systems due to their different radio interfaces and incompatible access protocols, they cannot provide the global roaming service. In addition, in order to provide a regional service to one mobile station as an integrated service, it is necessary to update the mobile station and add a new service.
However, as described above, for the existing mobile station, designing of an analog transmission/reception front-end unit and ASIC most suitable for the respective standards takes precedence over all things. Therefore, in designing a mobile station, hardware should be newly designed such that it can adapt to the various standards currently in development, and ASIC chips should be separately developed to be suitable for several standards for seamless roaming between standards and regions using one mobile station.
However, in the ASIC chip, complicated calculations, such as division, considerably increase the number of required gates, and modification of the ASIC chip due to a change in an algorithm is not simple. In addition, because the ASIC chip is a high-priced element realized with hardware, it cannot satisfy the low-power, small-size, low-price requirements of the mobile station. However, development of a new ASIC for supporting multiple standards requires great development time and cost. Therefore, in order to design a mobile station satisfying the foregoing requirements, it is necessary to introduce an open architecture based on Digital Signal Processing (DSP) and Software Defined Radio (SDR) technologies.